1. Technical Field
The disclosure relates to an image processing apparatus, an image processing method, and a computer-readable recording device, for performing positioning between a plurality of spectral band images obtained by capturing images inside a lumen by using rays of light having wavelength bands different from one another.
2. Related Art
In recent years, endoscopes have been widely used as medical observation devices that can noninvasively observe the inside of a lumen of a patient. As an imaging method used in the endoscopes, a sequential lighting and a simultaneous lighting are known depending on a difference in illumination method. The sequential lighting is a method of performing imaging by sequentially irradiating an object (inside of the lumen) with rays of light having wavelength bands different from one another to obtain a plurality of spectral band images.
In the sequential lighting, the timing of imaging of each spectral band image varies, so that a position shift (called a color shift) occurs between the spectral band images due to effects of contraction motion of the lumen or the like. The color shift could affect the observation of the inside of the lumen, so that positioning between the spectral band images may be performed.
As a technique related to the positioning between the spectral band images, Japanese Laid-open Patent Publication No. 2011-194151 discloses a technique of performing the positioning based on blood vessel information of each spectral band image. More specifically, blood vessels whose thicknesses are different from one another are emphasized by two types of spatial filters, and the emphasized blood vessels are assumed to be a blood vessel in a surface layer and a blood vessel in an intermediate layer, respectively. Then, the positioning between a short-wavelength spectral band image and an intermediate-wavelength spectral band image is performed by using position information of the surface layer blood vessel, and the positioning between the intermediate-wavelength spectral band image and a long-wavelength spectral band image is performed by using position information of the intermediate layer blood vessel.